Triple-L: Improving CPS Disk I/O Performance in a Virtualized NAS Environment

Network-attached storage (NAS) provides cyberphysical systems (CPS) with the scalable, efficient, and reliable backing storage, such as the mobile virtual desktop based on cloud infrastructure. Within this storage architecture, virtual machine (VM) instances running in the NAS client usually receive data from the complex physical world and then persist them in the neat cyberspace in the NAS server. In this paper, we propose Triple-L to improve VM disk I/O performance in the NAS architecture. According to the specific storage semantic, Triple-L decouples the VM image file into several subfiles at the host layer and then selectively moves them into the NAS clients. In such a way, a VM disk I/O request may be proceeded locally in the NAS client, instead of walking the external networking path repetitively between NAS server and client. We have implemented Triple-L in a Xen-based NAS system. An accessory solution for dealing with storage failure and VM live migration on Triple-L is also discussed and evaluated. The experimental result shows that our work can effectively improve the disk I/O performance of VMs. Meanwhile, it brings moderate overhead for VM live migration.